The present invention relates to a mica tape for an insulated coil used in electrical equipment such as rotating electric machinery, and also relates to an insulated coil. More particularly, the present invention is concerned with a mica insulated coil formed by a vacuum-pressure impregnation.
The insulated coil for use in high voltage rotating machinery is generally manufactured by steps of winding mica around a coil, impregnating the mica with a solventless thermosetting resin by a vacuum-pressure impregnation, and curing the resin with heat. As the mica tape employed in manufacturing such an insulated coil, a mica paper or an aramid fibrid mica paper has been used. The mica paper is formed, by a paper-making process, from fine mica particles and water alone. The aramid fibrid mica paper (hereinafter, referred to as "aramid mica") is formed, by mixing 5.+-.3 wt % of aromatic polyamide pulpy particles (hereinafter, referred to as "fibrid") in fine mica particles and subjecting the resultant mixture to a paper-making process, as described in Jpn. Pat. Appln. KOKOKU Publication Nos. 43-20421 and 1-47002.
The aramid mica contains fibrid, which is present among fine mica particles. Since the fibrid takes hold of the fine mica particles, the resultant aramid mica insulated tape is excellent in mechanical strength, heat resistance, and impregnation properties, as compared to a mica paper tape containing no fibrid.
As described above, the excellent insulation properties can be attained together with excellent heat resistance and impregnation properties by mixing the fibrid to the fine mica particles and subjecting the mixture to a paper-making process. However, the aramid mica has a problem in that it contains an aromatic polyamide. The aromatic polyamide is known to generate toxic hydrogen cyanide when it burns, since it contains nitrogen in its structural formula (see, for example, Proceedings of Electric & Electron Insulation Conf. 1987. VOL. 18th Page 181-187).
Therefore, when an insulated coil is manufactured by winding the aramid mica around a coil and impregnating the aramid mica with a solventless thermosetting resin in pressurized vacuum conditions, the insulated coil also generates the toxic hydrogen cyanide when it burns. The toxic hydrogen cyanide will be a significant problem to workmen's health. This problem makes it difficult to design a pollution-free recovering process of the conductive material from the insulated coil in order to obtain a recycle resource.